Connected: An Internet Encyclopedia
TELNET Protocol Overview

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### TELNET Protocol Overview

The TELNET protocol, designed for terminal-oriented remote login, is documented in RFC 854.

TELNET operates using the TCP Protocol, and depends heavily on option negotiation. TELNET options are documented in their own (usually short) RFCs. The organization of these RFCs, and intructions for registering new TELNET options, is found in RFC 855. Many TELNET options exist; a complete, current list can be found in the Internet Official Standards RFC, currently RFC 1880. A copy of this list appears below.

#### TELNET Options

    Protocol   Name                           Number  State Status  RFC STD
    ========   =====================================  ===== ====== ==== ===
    TOPT-BIN   Binary Transmission                 0  Std   Rec     856  27
    TOPT-ECHO  Echo                                1  Std   Rec     857  28
    TOPT-RECN  Reconnection                        2  Prop  Ele     ...
    TOPT-SUPP  Suppress Go Ahead                   3  Std   Rec     858  29
    TOPT-APRX  Approx Message Size Negotiation     4  Prop  Ele     ...
    TOPT-STAT  Status                              5  Std   Rec     859  30
    TOPT-TIM   Timing Mark                         6  Std   Rec     860  31
    TOPT-REM   Remote Controlled Trans and Echo    7  Prop  Ele     726
    TOPT-OLW   Output Line Width                   8  Prop  Ele     ...
    TOPT-OPS   Output Page Size                    9  Prop  Ele     ...
    TOPT-OCRD  Output Carriage-Return Disposition 10  Prop  Ele     652
    TOPT-OHT   Output Horizontal Tabstops         11  Prop  Ele     653
    TOPT-OHTD  Output Horizontal Tab Disposition  12  Prop  Ele     654
    TOPT-OFD   Output Formfeed Disposition        13  Prop  Ele     655
    TOPT-OVT   Output Vertical Tabstops           14  Prop  Ele     656
    TOPT-OVTD  Output Vertical Tab Disposition    15  Prop  Ele     657
    TOPT-OLD   Output Linefeed Disposition        16  Prop  Ele     658
    TOPT-EXT   Extended ASCII                     17  Prop  Ele     698
    TOPT-LOGO  Logout                             18  Prop  Ele     727
    TOPT-BYTE  Byte Macro                         19  Prop  Ele     735
    TOPT-DATA  Data Entry Terminal                20  Prop  Ele    1043
    TOPT-SUP   SUPDUP                             21  Prop  Ele     736
    TOPT-SUPO  SUPDUP Output                      22  Prop  Ele     749
    TOPT-SNDL  Send Location                      23  Prop  Ele     779
    TOPT-TERM  Terminal Type                      24  Prop  Ele    1091
    TOPT-EOR   End of Record                      25  Prop  Ele     885
    TOPT-TACACS  TACACS User Identification       26  Prop  Ele     927
    TOPT-OM    Output Marking                     27  Prop  Ele     933
    TOPT-TLN   Terminal Location Number           28  Prop  Ele     946
    TOPT-3270  Telnet 3270 Regime                 29  Prop  Ele    1041
    TOPT-X.3   X.3 PAD                            30  Prop  Ele    1053
    TOPT-NAWS  Negotiate About Window Size        31  Prop  Ele    1073
    TOPT-TS    Terminal Speed                     32  Prop  Ele    1079
    TOPT-RFC   Remote Flow Control                33  Prop  Ele    1372
    TOPT-LINE  Linemode                           34  Draft Ele    1184
    TOPT-XDL   X Display Location                 35  Prop  Ele    1096
    TOPT-ENVIR Telnet Environment Option          36  Hist  Not    1408
    TOPT-AUTH  Telnet Authentication Option       37  Exp   Ele    1416
    TOPT-ENVIR Telnet Environment Option          39  Prop  Ele    1572
    TOPT-EXTOP Extended-Options-List             255  Std   Rec     861  32

Connected: An Internet Encyclopedia
TELNET Protocol Overview